Genes for Normal Behavioral Variation Recent Clues from Flies and Worms

(see Tully, 1996). These behavioral geneticists were inThe question of how genes contribute to normal individterested in why individual differences in behavior had ual differences in behavior has captured our imagination evolved and how variation is maintained in natural popufor more than a century. Several fundamental questions lations. Most often, they found that many genes (polycome to mind. How do genes and their proteins act in genes) contributed to the behavioral differences bethe nervous system and in response to the environment tween the artificially selected strains. It was assumed in order to cause individual differences in behavior? Do that each polygene had small, cumulative effects on genetic differences between natural variants arise from the behavioral phenotypes and that they were therefore alterations in the structural or regulatory regions of a unmappable. The three papers that will be discussed in gene? Can we predict which genes for behavior, identithis minireview prove that major gene effects are refied by mutant analysis in the laboratory, will have natusponsible for some natural variation in behavior and that ral allelic variation? Three groundbreaking studies (Osthe molecular basis of these genes can be understood. borne et al., 1997; Sawyer et al., 1997; de Bono and They demonstrate that studies of natural variants do Bargmann, 1998) published in thepast year demonstrate provide insight into both the mechanistic and evolutionthat we now have the knowledge and technological caary significance of normal variation in behavior. pability to address these questions empirically. Each In Sawyer et al. (1997), natural variation in a behavioral study has successfully identified a single major gene for phenotype was shown to result from a molecular poly-